The present invention relates to a video coding method of exploiting the temporal redundancy between successive frames in a video sequence.
Efficiently encoding video or moving pictures relies heavily on exploiting the temporal redundancy between successive frames in a sequence. Based on the assumption that local motions are slow with respect to the temporal sampling period, several techniques have been proposed for efficiently removing this redundancy. The most successful and acclaimed method is block-based motion prediction, heavily used in nowadays standards such as MPEG4 and H.26L. Roughly speaking, these compression scheme predict a frame in the sequence based on the knowledge of previous frames. The current frame (or predicted) is cut into blocks of fixed size and the best matching block is searched in the reference frame. Displacement vectors are then encoded so that the decoder can reconstruct the prediction of the current frame from the previously decoded frame(s). As the block-based prediction is not accurate enough to encode perfectly the current frame, the error between the original and the predicted frame is encoded separately. This is in general referred to as texture coding or motion residual coding. The main draw-back of this method lies in the blocky nature of the prediction mechanism, which gives rise to very noticeable blocky artefacts at low bit rates. Moreover such a system, while well suited for wide translational motions, is unable to cope with locally complex movements or even global geometric transformations such as zoom or rotation. Finally, block based motion prediction is not able to follow natural features of images since it is stuck in a fixed framework based on artificial image primitives (blocks).